AbstractThe temperature dependence of the polymerization rate is investigated using the NCA's of β‐benzyl L‐aspartate and γ ‐benzyl L‐glutamate. Activation energies for polymerizing the above NCA's are 13 and 9 Kcal per mole, respectively. Entropies of activation and Arrhenius constants, A, are also calculated and discussed in terms of the polymerization mechanism. The significance of the proton‐transfer reaction in the “active monomer” mechanism is recognized through a kinetic isotope effect and also by comparing the polymerization rates of L‐alanine NCA and its structural analog L‐alanine N‐thiocarboxyanydride. It is theorized that a changing position of equilibrium of the neutralization step decreases the concentration of “active monomer”, thereby slowin